1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method wherein a light beam from a light source is modulated according to an image signal from a controller while the light beam is scanned in a main-scan direction by means of an oscillation mirror in resonant oscillations thereby forming a latent image on a latent image carrier.
2. Description of the Related Art
In electrophotographic image forming apparatuses such as printers, copiers and facsimiles, an image forming command is applied to a controller from an external apparatus such as a host computer responding to a request from a user wanting to form an image. The controller in turn converts the image forming command into data in a format suitable for directing operations of an engine. The engine is controlled based on the data, so as to form an image corresponding to the image forming command on a sheet (recording material) such as copy sheet, transfer sheet, paper or transparent sheet for OHP. Specifically, a light source of an exposure unit in the engine emits a light beam modulated in correspondence to the image data, as ON/OFF controlled based on the image data included in the image forming command. The light beam is scanned in the main-scan direction by means of a deflector of the exposure unit, thereby forming a latent image corresponding to the image data on a latent image carrier such as a photosensitive member. Then, the latent images are developed with toners so as to form toner images.
Aiming at downsizing and speeding up the deflector, it has heretofore been proposed to employ a resonant oscillation mirror as the deflector, the oscillation mirror disclosed in, for example, Japanese Unexamined Patent Publication No.1-302317. In this apparatus, the oscillation mirror is driven into resonant oscillations by matching a frequency of a drive signal applied to the oscillation mirror (hereinafter, referred to as “drive frequency”) with a natural resonant frequency of the oscillation mirror, whereby a relatively great amplitude is attained. The light beam from the light source is guided to the oscillation mirror in resonant oscillations so as to scan the light beam.